Telephone system.



PATENTED SEPT. 25, 1906.

1?. G. BELL. TELEPHONE SYSTEM.

APPLIOATION FILED 001.9, 1905.

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PATENTED SEPT, 25, 1906.

F. G. BELL. TELEPHONE SYSTEM.

APPLICATION FILED 0GT.9,1905.

6 SHEETS-SHEET 2.

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PATENTED SEPT. 25, .1906.

F. G. BELL.

TELEPHONE SYSTEM.

APPLICATION FILED OCT.9, 1905.

6 SHEETS-SHEET 3.

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No. 831,819. PATENTED SEPT. 25, 1906. PG. BELL.

TELEPHONE SYSTEM. APPLICATION FILED 0019, 1905.

6 SHEETS-SHEET 4.

flame t No. 831,819. I PATENTED SEPT. 25, 1906. P. G. BELL.

TELEPHONE SYSTEM.

APPLIGATION FILED 002m, 1905.

8 SHEETS-SHBET 5.

No. 831,819. PATENTED SEPT. 25, 1906.

P. G. BELL. TELEPHONE SYSTEM.

APPLICATION FILED OGT.9, 1905.

6 SHEBTS-SHEET 6.

UNITED STATES PATENT EEroE.

FRANCIS GEORGE BELL, OF LONDON, ENGLAND, ASSIGNOR OF ONE-HALF TO ISIDOREBERNARD BIRNBAUM, OF LONDON, ENGLAND.

TELEPHONE SYSTEM.

No. s31,e19.

Specification of Letters Patent.

Patented Sept. 25, 1906.

Application filed October 9 1905. Serial No. 281,974.

To all whom it may concern:

Be it known that LFRANGIS GEORGE BELL, electrical engineer, a subject ofthe King of Great Britain, residing at 200 Upper Thames street, in thecity and county of London, England, have invented new and usefulImprovements in or Relating to Telephone Systems, of which the followingis a specifica tion.

This invention relates to telephone-exchange systems working with acommon battery; and it has for its object to simplify and improve theindicating and switchboard arrangements and the calling and connectingapparatus of such systems.

According to this invention the line-indicator is made simultaneously toserve as a clearing-out indicator and impedance-coil and in some casesalso as a translator and as a self-inductor for a special callingapparatus.

Further, the arrangement of the operators set is improved and a novelmethod of constructing and wiring the through communication-plugs isintroduced, whereby a telephone system well balanced and arranged as awhole is secured.

In the accompanying drawings, Figure 1 shows two subscribers stationsand the connections therefor at the switchboard in one arrangement inaccordance with the invention. Fig. 2 shows the operators set for usewith the switchboard shown in Fig. 1. Fig. 3 shows the throughconnecting-plugs. Fig. 4 is a diagram illustrating the connections whenthe operator is speaking with a subscriber. Fig. 5 shows the connectionswhen two subscribers are in conversation. Fig. 6 shows a modifiedarrangement at the subscribers station for calling with earth-return orcommon-return connection. Fig. 7 shows the arrangement of the operatorsset for use when the subscribers set is as in Fig. 6. Fig. 8 shows amodified arrangement at the switchboard. Fig. 9 shows the operators setas modified for use with the switchboard arranged as in Fig. 8. Fig. 10is a diagram of the connection when two subscribers are talking withthis modified arrangement of the switchboard. Fig. 11 is a diagram ofthe operators set with "simple impedance and with the special callingapparatus applied thereto. Fig. 12 illustrates the connections for theboard shown in Fig. 1 when the operator is calling a subscriber by thearrangement shown in Fig. 11. Fig. 13 is a diagram of the operators setwith split impedance y" j and with the special calling apparatus appliedthereto. Fig. 14 similarly illustrates the connections for the apparatusas in Fig. 8 when the operator is calling a subscriber with theapparatus shown in Fig. 13. Fig. 15 shows the special calling apparatusapplied in a somewhat difl'erent way in the operators set.

In the arrangement shown in Fig. 1 the subscribers stations I II areconnected by pairs of line-wires with pairs of terminals a b on theswitchboard. It will be convenient to refer to the lines as the a, lineand 1) line, respectively, which are connected to the a and 1) terminalsin each case and to letter all terminals connected to said lines as aand b, respectively. Each subscribors set includes a receiver 1',transmitter 25, hook-switch it, (operated by hanging up and taking downthe receiver,) and a hell i, bridged across the a and b lines by acondenser It, so that said bell can answer to alternating or pulsatingbut not to continuous currents.

There is a spring-jack 0n the switchboard for each subscriber, each jackhaving two movable springs c and f and three fixed springs or contacts(Z, 6, and g. In front of each jack also is a collar Z in directelectrical connection with the terminal of the a line. An indicator m isconnected between the fixed spring f in each jack and the a line, whilethe movable spring 0 in each jack is directly connected to the b-lineterminal. Each indicator is of the type in which the dropplate isdirectly operated by the armature 9 and which therefore continues toindicate so long as a current passes through the indicator-coils. Thedrop does not return to its non-indicating position until the flow ofcurrent through the coil ceases and the armature is released. Thearmature 9 preferably touches a back contact 10 at all times when saidarmature is not attractedby the electromagnet m. The object of this isexplained below.

The indicators have their coils wound on cores, so that said indicatorswill serve also as impedance-coils for the battery-circuits. No otherimpedance-coils are necessary in the speaking-circuits. 0 is the commonbattery of a suitable number of cells according to the size of thetelephone-exchange which'itoperare a and 5 terminals connected,respectively, -with the sleeves s and tip p of the operators' plug.'When this plug is inserted in ajaClg-the-sleeve 8 contacts with collarZ and is thus-connectedwiththe subscribers a lineywhile the tip ppresses back the spring a, connected to the subscribers Z) line. Theoperators a terminal is connected, on the one hand, through the receiver1", key q, transmitter t,--an'd impedance-coil with the terminal 2,connected to the (zinc) terminal of the common battery 0. It is alsoconnected by wire 3 with the calling-generator u, the switch '2) ofwhich is normally connecting the b terminal to the impedance-coil j, butwhich "automatioa'llyconnects said terminal I) to the generator itduring calling in well-known manner.

The-pair of'through connecting-plugs 1 2 .(shown -inFig."3)are'used toconnect two subscribers. One plug differs from the other inthat' one,-1, hasa sleeve sand tip p only, while the other, '2, hasasleeve s, aring w, and a" tip p. These parts in each plug are ofcourse-insulated,*and the tip p of-plug 1 is connected to the sleeve 8of plug 2, as shown,

i whilethesleevesof plug 1 is connected to the ringw of plug 2. The tipof plug 2 has no electric connections, as it serves only-as a mechanicaldevice to operate the inner springfof one jack in any pair placed inconnection. The-sleeves-s always enter the collars Z,'while' the tip ofplug 1 (and of the oper- -atorsplug)--and the ring w of plug 2 alwayspress against the spring 0 of any jack in which they are inserted.

In operationwith this system the battery '0isnOrmallyconnected, as willbe seen, on the side through the springs e f of the jacks withthe wlines of all subscribers stations and on the side through the relay nand springs "d c with the 5 lines; but owing to 'theuse -of a condenserk at each station no current can'pass in" any of the circuits. As soon,howevergas-a subscriber'e. g.,"at station- Ireinoves his telephone fromthe hookswitch-Zr or otherwise closes his line-circuit the current ofthe common batteryo passes over'his a and b'lines through his station bythe contacts between springs cf and d c of the j'acks,'--as abovementioned, and thus the relay or -audible signaling device eat thecentralstation is-operated. The operator hearing the "relay signal andseeing the particular drop-signal of the indicator m of the station (I)which is calling, inserts her plug into the jack of the saidcalling-station; but as said ator presses the key q, connecting hertele-,

phone set between her a and .2 terminals, and the speaking-circuits arethen, as follows: from the terminal of battery 0 through the springs e fin jack I and through the indicatorcoil m of the station I which hascalled. From this point there are two paths'open. The first is throughthe subscribers line-wire a and his telephone set back byline b to'thejack, through the spring 0 therein, the tip 19 of the operators plug,operators terminal b, the spring contact-switch '0 of the generator inthe operators set, the impedance-coil j, and back tothe terminal of" thebattery 0. The second path is from the indicator-coil m through thecollar Z of the jack, the sleeve 8 of the plug, operators a terminal,through opertors telephone set, the key (1 of which is closed, and'theimpedance-coil 7' back to the battery terminal. Fig. 4 showsdiagrammatically the circuits whichare now closed, and it will be seenthat the impedance-coil j balances the indicator mat the side ofthecircuit next to the battery terminal, and asa perfect balance'is thusobtained speaking can be effectually carried on between the operator anda subscriber. As will be seen later, (see Fig. 5,) the indicator-coil mof a second subscriber serves'the purpose of the impedance-coil 7' whentwo subscribers'are connected through to one another.

After receiving and answering a call the operator rings up the desiredstationsay IIby inserting her plug into theja'ck II of said station'andoperating the calling-generator u. The alternating current generatedthen passes from the generator u and a terminal of the operatorssetthrough the collar Z of the ack II directly through the'lines a, and Z)of station II' and itscondenser Zr and call-bell i and through thespring a of the jack, tip p of plug, operators terminal b, and automaticswitch 1) back to the generator u.

The call having been given and answered the operator connects the twostations'by the through"connecting-plugs 1-and'2. "The plug 2, havingasleeve 8, ring w,-and tip 10, makes contact with thecollar Z and spring0 of its jacksay Iwhile simultaneously its tip 29 presses overthe'spring f from spring 6 to make contact with spring g,-so that theindicatorm of station I is disconnected from the terminal of the commonbattery and is connected'instead with the terminal. At the other jack IIthe plug 1 having only a sleeve 8 and a tip the spring f, connected withthe indicator m, remains in contact with spring 6 and is thus inconnection with the battery terminal, while the sleeve 8 takes contactwith the collar Z, connected to line a, and the tip p with the spring 0in the jack connected to the line 1), this latter spring being thuspressed back away from spring (Z. The speakingcircuits (indicateddiagrammatically in Fig. 5) are now as follows: from the terminal ofbattery 0 through springs e and f of jack II, indicator m, after whichthe circuit is branched. The one branch goes over the a line to stationII, through the instruments at that station back by the 1) line tospring 0 in the II jack, tip 1) of plug 1, and through theconnecting-lead to sleeve 5 of plug 2, thence from collar 1 of jack Ithrough indicator m of station I, springs f and g, (pressed together bythe tip of plug 2,) and so back to the battery terminal. The otherbranch is from the indicator m of station II through the collar Z ofjack II, sleeve 8 of plug 1, and by the connecting-lead to ring to ofplug 2, spring 0 of jack I, the 1) line of station I to that station andback by the a line through indicator m of station I to springs f and g,as before, to the battery terminal. It will be seen particularly clearlyin Fig. 5 how exactly balanced the whole speaking system is with theseconnectionsthe two stations are connected in parallel between theterminals of the two indicators m m thus brought into action, and thehighfrequency speaking-currents of course pass through the two stationsas if they were directly connected in series. The indicators m, asbefore mentioned, have drops which only remain raised or visible so longas a current is passing, so that said indicators will return to theirnormal position when the current ceases to flow through them. It will beseen that this will not occur when the subscriber at one station onlyhas hung up his receiver or otherwise broken his circuit, because, asseen in Fig. 5, the battery-current will continue to flow through bothindicators m and one station even after the other is cut off. It,therefore, no special clearingsignal were giveni. e., if the backcontacts 10, explained below, were omitted-the indicators would serve togive the clearing-out signal, showing when both subscribers had finishedtheir conversation, because the two indicator-drops would simultaneouslyreturn to their non-indicating position as soon as both subscribers hadhung up their telephones; but the indicators are preferably arranged togive a clearing-out signal, as follows: The back contacts 10 ofarmatures 9 are connected to the 7) terminals in each case, and thearmatures 9 themselves are all in electrical connection through therelay n with the battery terminal. The armatures normally rest againstthe contacts 10, as before explained but there can be no circuit throughthese contacts unless the through connecting-plugs 1 and 2 are in twojacks and the subscribers thus connected are not communicating. This iseasily seen, for as long as a subscribers telephone is on the hook itthere is no circuit through his station, and the parts of theswitchboard connected to the battery terminal i. 6., jacksprings c andf, indicator-eoils m, a lines, and collars Z-are insulated from all theother parts which are connected with the terminal. As soon as theoperator closes a circuit through his station his indicator operates,breaking the contact at 10. Further, if the through connecting-plugs arein two jacks the indicators of both jacks remain operative, and thecontacts at 10 are broken until both subscribers hang up theirtelephones. Then, however, the following oc curs: The armature of thejack in which the plug 2 is inserted falls, because the spring f in thatjack is pressed away from the spring a and there in no longer aconnection through the other station and the collar Z with the batteryterminal. Hence the contact 10 is closed by armature 9 of the indicatorm in this jack. The same would happen in the other jack were it not thata circuit is now closed through the spring a and spring f in this jack(in which plug 1 is inserted) through the indicator m of this jack,collar Z, plug-lines to spring 0 in the first-mentioned jack, (in whichplug 2 still is,) and thence through contact 10 and armature 9 to relayn and the battery terminal. Hence the relay n will give a clearingoutsignal calling the operators attention to the fact that the conversationis finished and the relaysignale. 9., sounding ot a buzzer will continueto be given until the operator pulls out the through connecting-plugs,and thus breaks the circuit.

The system can be equally'well arranged for working with a common returnin the calling-circuits, each station then having a third terminalconnecting the bell with such commen-return line or earth, while onegeneratorterminal is connected to said return line or earth, as the casemay be.

Figs. 6 and 7 show the modifications in the subscribers stations and theoperators set, respectively, for this purpose. At the subseribersstations the switches h have contacts at, which they rest against whenthe receivers are on the hooks, and the bells i are connected to thesecontacts, on the one hand, and to earth or a common return 1 on theother hand. In the operators set the wire 3 is similarly connected to acommon return or earth 1 instead of being connected with the wire fromthe a terminal. The ringing in this case is effected by the generator atover the 1) terminal of operators set, operators plug-tip p, subscribersjack-spring c, b terminal, 1) line to hook-switch h at subscribers'paratus, as explained below.

set, and (as the receiver is on the hook) by contact x through the belli to the common return or earth 1 The speaking-circuits remain asbefore.

Where it is required to have translators in order to obtain inducedspeaking-currents capable of operating over long distances, the

indicators m may be arranged to work as translators. In such case theindicator-coils are split, so that the current going to one stationpasses through one part of the coil and the current to the other stationthrough the other part. Each portion then serves as a translator for theother. This is shown in Figs. 8, 9, and 10, which correspond with Figs.1, 2., and 5, above explained, for the simple type of indicator. Thearrangement of Fig. 8 differs from that of Fig. 1 only in that theindicators have split windings m m connected, respectively, with the aterminal and the collar Z. In the operators set, Fig. 9, the arrangementdiffers from that of Fig. 2 only in that the impedance-coil is splitinto two parts j P, with the connection to the terminal 2 between them,while the part 3" is connected to the speaking instruments t and r andthe part 3' to the generator-switch v. The calling and speaking circuitswith this modified arrangement are substantially the same as with thefirst-described arrangement, the only difference being that each of theparallel battery-circuits during speaking contains the parts m of oneindicator and m of the other, or one of the impedance-coil parts 9" 3'in place of one of the indicator parts. The diagram Fig. 10 will makethis clear. In speaking, the high-frequency current in one part'of theindicator-coil serves to induce corresponding current impulsesin theother part, and these impulses will operate effectively in the receiversof stations at considerable distances. In this case, therefore, thecalling-indicators serve also as impedance-coils, clearing-out indicators, and translators. They may further serve as self-inductors in aspecial calling ap- If there are no back contacts 10 to armatures 9, theclearingout signal is only a visible one given by both drops oftwocommunicating stations falling back simultaneously when the secondsubscriber hangs up his telephone, as before explained with reference toFig. 1. If, however, the contacts 10 are provided, the relay n is causedto give an audible or other suitable clearing-out signal, as alreadyexplained.

With the special calling apparatus about to be described amagneto-generator becomes unnecessary in the operators set. Fig. 11shows one arrangement for the purpose. The talking instruments 7" t andthe key g are in lines normally connected between the operators a and 6terminals, with a connection through the impedance y tothe 2 terminal,and a key 4 is provided for cutting out the speaking set and connectinga vibrator across the lines. This vibrator is similar to that used in anelectric bell L. 6., it has an electromagnet 5 and an armature 6,adapted to alternately make and break the circuit of the magnet. Withthis device after the operator has plugged in to the line to be calledshe has only to press the key 4. Current from the common battery 0 thenpasses through the springs e and f of the jack of the station to becalled, the indicator m, the collar Z, sleeve 8 of operators plug to thea terminal of the operators set, thence through the contact of armature6, the coils of electromagnet 5, the key 4, and impedance-coil j to the2 terminal of the operators set and so to the terminal battery. -Thearmature 6 is thus attracted by the magnet 5 breaking the circuit abovementioned and stopping the flow of batterycurrent. The magnet is thusdenergized, the armature makes'contact again, and a vibrating action isthus set up just as in an electric bell. At every break of the circuitduring the vibration a very powerful self-induced current will be set upin the indicator and impedance-coils, and this current passes throughthe a and 1) lines of the subscriber to be called and acts through thecondenser is to ring a polarized bell t at the subscribers station.

Fig. 12 shows a diagram ofthe connections when simple'indicator-coils mand impedancecoils j are used. The'battery-current when it flo WS passesthrough the indicator and .impedancc coils in the reverse direction tothat of the self-induced current, and consequently the self-inducedcurrent of the indicator-coil is assisted and increased by theself-induced current in the impedance-coil, and vice versa. Fig. 18shows the operators set for calling with the special apparatus whensplit impedances j y' are used, and Fig. 14 gives a diagramcorresponding with Fig. 12, but showing the operators splitimpedance-coil and the subscriber s split indicato coil m" m The actionin this case is similar to that of Fig. 12.; but the current impulsesinv the subscribers calling'circuit on break in the operatorsbattery-circuit are due to a large extent to actual induction fromindicator-coil m to coil m and impedance-coil y" to coil The advantageof this method of calling lies partly in the saving of the cost of anexpensive generator and partly in the con- IIO venience which resultsfrom the giving of the call by simply pressing a key insteadof byturning a generator-handle.

' The self-inducing effect would be obtained. in the calling apparatusif the impedance-coil of the operator s set were omitted or if a simpleimpedance 1, as in Fig. 1 1, were used with double indicator-coils m mand I do not, therefore,zlimit myself to the use of such a coil or anyone type of coil with this special calling device; but said device isapplicable to all common-battery telephone installations in which thereare impedances of suitable I3 the key (1 untouched, and the vibratingtype in connection with the line-circuits, either in the to rm of theindicators or as separate impedance-coils.

I desire to make it clear that I do not limit myself to any particularmechanical devices for effecting most of the operations hereinbeforementioned.

The system is applicable to subscribers sets of any type now usual. Therelay or other commonsignaling apparatus at the central station may alsoof course take a number of forms and may give a visible or other signal,as is desired, and although I prefer the well-balanced arrangementwherein the two indicators are on opposite sides of the battery bothindicators may be in some cases arranged on one side of the battery,while the other features of my invention and the calling arrangementwhich are applicable in such cases are retained. The device illustratedin Fig. 15, for example, is .claimed to be within the scope of thisinvention. Fig. 15 shows one or two small modifications of the specialcalling apparatus. In this case an additional battery 7 is provided inthe operators set for increasing the strength of the callingcurrent, andin place o1 a separate switch 4 for operating the calling apparatus aback contact is provided at 8, against which the operators hand-key qrests in its normal position. The calling-circuits are the same as abovedescribed, the only difference being that the battery 7 provides morecurrent, if required, while the back contact 8 makes it possible for theone key (1 to be used for both calling and speaking purposes. Theoperator with this device has only to plug into the jack of thesubscriber to be called, leaving apparatus 5 6 will give the requiredcall. By pressing the key (1 the operator will bring herself intospeaking communication with the called station while simultaneouslycutting out the calling apparatus 5 6. Similar arrangements areobviously applicable with split impedance-coils, as in Fig. 13; but itis needless to go further into such details.

hat I claim is 1. In a common-battery telephone system, the combinationof the battery, the sub scribers stations and c'onnectinglines, aswitching apparatus and an indicator at the central station inconnection with each subscribers station, and means for connecting theswitching devices to bring two subscribers into communication, theswitching apparatus, connecting means and indicators all being such thatthe two indicators of two communicating subscribers will be connectedbetween the battery and the subscribers stations one indicator at eachterminal of the battery and that the two indicators will both remain onthe lines when a conversation is proceeding, will serve together to givethe line indications, the clearing-out signals and will also serve asimpedance-coils in the system.

2. In a common-battery telephone system, the combination of the battery,the subscribers stations and connecting lines, a switching apparatus,and an indicator at the central station in connection with eachsubscribers station, an operators set including an impedance-coil andcalling apparatus, and means for connecting the switching devices tobring the operator and a subscriber, or two subscribers intocommunication, said switching apparatus, connecting means and indicatorsbeing such that the indicators, or one indicator and the operatorsimpedancecoil, will become connected to opposite terminals of the commonbattery with the two telephone sets in parallel between the terminals ofthe indicators, or the indicator and impedance-coils, and that theindicators will serve to give the line indications, the clearingoutsignals, and will also serve as impedancecoils.

3. In a common-battery telephone system, the combination of the commonbattery, the subscribers stations and connecting-lines, indicators atthe central station each in connection with one subscribers lines,switching devices each in connection with one subscribers station andwith the indicator there- 9 5 for and adapted to normally connect saidin dicator with one terminal of the common battery, and meansforconnecting any two stations through their switching devices, said meanssuch that the indicator-of one connected station has its connectionchanged from one terminal of the common battery to the other when theconnection between two stations is made. 4. In a common-batterytelephone system, the combination of the common battery, the subscribersstations and connecting-lines, indicators at the central station each inconnection with one subscribers lines, acks each having springsrespectively in connection with the common-battery terminals, theindicator and the lines of one subscribers station, and a pair of plugswith connectingwires, said plugs adapted to be inserted in the jacks toconnect two stations, and one of said plugs adapted to change theconnection of the indicator through its jack from one terminal of thecommon battery to the other. 5. In a common-battery telephone system,the combination of the common battery, the subscribers stations andconnecting-lines, indicators at the central station each in connectionwith one subscribers line, jacks each having springs respectively inconnection with the common-battery terminals, the indicator and thelines of one subscribers station, and a pair of plugs withconnectingwires, said plugs adapted to be inserted in. the acks toconnect two stations, said plugs and connecting-wires such that theyconnect one terminal of thecommon battery through i the coils of onesubscribers indicator to the subscribers stations in parallel, andthrough said stations to the other subscribers indicator,'through thecoils of said indicator back to the other terminal of the commonbattery, whereby'a balanced communicating system is produced.

'6. Ina common-battery telephone system, the combination of the battery,the subscribers stations and connecting lines, a switching apparatusandan indicator at the central station in connection witheachsubscribe'rs station, a signaling-relay and means connecting'it withthe battery and switching devices, 'mea'ns'for connecting the switchingdevices, to bring any two subscribers stations into communication, andconnections adapted to'be made by the indicators when not indicat ingsuch that a battery-circuit is established through the switching devicesand means connecting s'am'e,and through'the signalingrelay when bothsubscribers have broken their speaking lines, whereby a clearing-outsignalcontrolled by the indicator is' given by the signaling rel'ayuntil the connection between'the'switching devices-is broken.

'7. In a common-battery telephone system, the combination of the commonbattery, the subscribers stations and connecting-lines, indicators atthe centralstation each in connection with one subscribers lines, jacksea'ch'h'aving'springs respectively in connec tion withthe common-batteryterminals, the indicator and the lines of one subscribers station, "apair of plugs with connecting-wires, said plugs adapted to be insertedin the jacks to connect two stations, a signaling-relay and means forconnecting it to the battery and to a part in each jack, and connectionsadapted to be'madeby'the indicators when not indicating such that acircuit is established from one battery-terminal through part of onejac-k,'the through connecting-plugs, part of the other jack,'and'throughthe signalingrelay back to the other battery-terminal when bothconnected subscribers break their speaking-circuits, whereby, 'aclearing-out signal controlled by the indicator is given which persistsuntil the through connectingplugs'are withdrawn.

8. In a common-battery telephone system, the combination of the commonbattery, the subscribersstations and connecting-lines, indicatorseachincluding two coils wound on the core, one'of said indicatorsconnected to the-line of eachsubscriber, switching devices one inconnection with each subs'eribers station and the indicator thereof, andmeans for connectingthe-switching devices of'any two stations, saidmeans and switching devices such that th'e'stations'are connected to thecommonbatter'y in parallel circuits each with one coil of one indicatorand one coil of the 5 other included therein, whereby theindicaswitching devices of any two stations, said connecting means suchthat two stations, or the operators set and one station, may'beconnected thereby to the commonbattery in parallel circuits each circuitincluding one coil of one indicator and one coil ofthe other or of thesplit impedance, whereby balanced speaking-circuits are produced.

10. In a common-battery telephone s'ys-.

tem, the combination of the common battery, the subscribers stations andconnecting-lines, indicators each includingtwo coils wound on thecore,'one of saidindicatorsconnectedto the line of each subscriber,switching devices one in connection with each subscribers station andthe indicator thereof, a signaling-re lay andmeans connecting it withthe battery and switching devices, means for connecting the switchingdevices of any two stations, said means and switching devices such as toconnect the subscribers sets and halv'es of'the indicators in parallelbalanced circuits on the terminals of the common battery, andconnections adapted tobe'm'ade by'the indica-- tors when not indicatingsuch that a batterycircuit is established through the switching devicesand means connecting *them and through the relay when both subscribershavebroken their speaking-lines, whereby a clearing-out signal isgivenby the relayuntil the connections between the-switching devices arebroken.

11. In a telephone system the combination of a common "battery, thesubscribers stations each including telephone instruments and an audiblesignaling apparatus, connecting-lines for the subscribers stations, anoperators set including a vibrator "and key therefor, adapted to connectsaid vibrator directly across the operator s telephone-wires,an'impedance, and means for connecting the operators set andasubscribers lines in parallel to the terminals of the common batterythrough the impedance, whereby the pulsations of current allowed topassthrough the battery and im edance by the vibra-torare enabled to prouc'ecurrent impulses inthe subscriberslines which impulses in turnoperate the subscribers signaling'apparatus.

12. In a telephone system the combination of a common battery, thesubscribers stal in communication in such a way that the pultions eachincluding telephone instruments and an audible signaling apparatus,connectinglines for the subscribers stations, an operators set includinga vibrator and a key therefor adapted to connect said vibrator directlyacross the operators telephone-wires, indicators the coils of which areadapted to act as impedances in connection with each subscribers lines,and means for connecting the battery and one indicator-coil in parallelto the operators and one subscribers sets, whereby the pulsations ofcurrent allowed to pass through the battery and coil by the vibrator areenabled to produce current im pulses in the subscribers lines whichimpulses in turn operate the subscribers signaling apparatus.

13. In a telephonesystem the combination of a common battery, thesubscribers stations each including telephone instruments and an audiblesignaling apparatus, connecting-lines for the subscribers stations; anoperators set including a vibrator and key therefor, means forconnecting the operators set to a subscribers lines, an impedance-coilin the operators set, indicator-coils in connection with the lines ofeach subscribers station, and means for connecting the battery betweenthe impedance-coil and indicator of the operators set and subscribersstation respectively which are in communication, whereby the pulsationsof current allowed to pass by the vibrator are enabled to producecurrent impulses in the lines which impulses in turn operate thesubscribers signaling apparatus.

14. In a telephone system the combination of a common battery, thesubscribers stations each including telephone instruments and an audiblesignaling apparatus, connecting-lines for the subscribers stations, anoperators set including a vibrator and key therefor, means forconnecting the operators set to a subscribers lines, a splitimpedancecoil in the operators set, split indicator-coils in connectionwith each subscribers lines, and means for connecting the batterybetween the impedance and indicator coils of the operators andsubscribers sets which are sations of current allowed to pass by thevibrator through one circuit are able to produce, in the impedance andindicator coils, induced current impulses in the other circuit capableof operating the subscribers signaling apparatus.

15. In a telephone system the combination of a central battery,subscribers stations each including telephone instruments and audiblesignaling apparatus, indicators with split coils, one indicator for eachsubscribers set, an operators set including a vibrator and key therefor,means for connecting the operators set and a subscribers station inbalanced parallel circuits on the centralbattery terminals, means forconnecting two subscribers stations in balanced parallel cir cuits onthe central-battery terminals, a sig naling-relay at the centralstation, and means controlled by the indicators and station-connectingmeans for closing the circuit of the relay when two communicatingsubscribers break their speaking-circuits.

16. In a telephone system the combination of a common battery, thesubscribers stations each including telephone instruments and an audiblesignaling apparatus, connecting-lines for the subscribers stations, anoperators set including telephone instruments, a vibrator, a two-way keyadapted to connect either the telephone instruments or the vibrator tothe line-wires of the operators set, an impedance, and means forconnecting the battery and impedance in parallel to the operators andone subscribers sets, whereby the pulsations of current allowed to passthrough the battery and impedance by the vibrator are enabled to producecurrent impulses in the subscribers lines which impulses in turn operatethe subscribers signaling apparatus.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

FRANCIS GEORGE BELL.

IVitnesses IIUBERT A. GILL, LEON E. IIAYNES.

